Oscillator mode suppression



Aug. 21, 1951 w. ALTAR ET AL 2,565,112

OSCILLATOR MODE SUPPRESSION Filed Dec. 27, 1947 Pea a; tance Material WITNESSES: INVENTORS William HZ far and M John W Coltman BY 72. 4. W

Patented Aug. 21, 1951,

William Altar and-John w, Coltman, Pittsburgh, Pa., assignors to Westinghouse Electric Oorporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 27, 1947, Serial No. 794,176

Claims.

Our invention relates to generators of electrical oscillations and, in particular, relates to an arrangement adapted for use in generating pulsed electrical oscillations of ultra high frequency.

Generators of ultra high frequency oscillations,

of which the magnetron may be taken as an example, embody, as part of their structure, chambers or cavities which tend to resonate at the frequency of the electrical vibrations being generated. However, as is well known, such resonant cavities are capable of vibrating in a number of different modes of vibration, with a corresponding range of different frequencies; and the same is true of the wave guide and resonator systems through the agency of which they supply power to load devices. Since the generators are thus capable of oscillating at a number of different frequencies, it is sometimes difiicult to induce generation at a particular one of these frequencies which maybe desired, inasmuch as substantial energy is involved in vibration in any mode, and the amount of such energy is considerably greater in the case of some modes than in the case of others. Difficulty thus arises in inducing the oscillation generator to build up the mode of vibration which may be desired in any particu lar case. Factors which determine the rate of building up energy in the respective modes include the size of the cathode, for example, in magnetrons, the operating voltage and current, the type of electric field pattern readily realizable in the tube and connected transmission systems, and the noise level which usually furnishes the initiating vibratory energy. By adjusting one or more of these to give a high conversion efiiciency for the desired mode of vibration, it is in many cases possible to enforce such mode. However, in other cases such adjustments are either more or less ineffective or interpose difiiculties of an undesirable character in a particular practical application of the generator. Where, as is now frequently the case, it is desired to employ such generators for sending out energy in the formof successive pulses of short duration, separated from each other in time, it is obvious that the necessity for building up the desired mode of vibration exists each time a new pulse is generated, and that the difficulties above described are particularly acute in the case of such uses.

One object of our invention is, accordingly, to provide an arrangement which enforces a particular desired mode of oscillation on an ultra high frequency generator system.

Another object of our invention is to provide an arrangement in which the desire mode of 2 vibration is forced to build up in an oscillation generator by injecting power at the frequency corresponding to the desired mode from an ex-i ternal source into the generator system.

Stillanother object of our invention is to materially shorten the time required for causing a generator of ultra high frequency vibrations to build up its energy in the desired mode of vibration to a level sufficient to insure maintenance of that vibration mode when connected to a work device. ,7 Still another object of our invention is to provide an improved form of generator for ultra high frequency electrical vibrations.

A still further object of our invention is to provide a novel type of ultra high frequency generator employing the magnetron principle of generation.

Other objects of our invention will become apparent upon reading the following description,- taken in connection with the drawing in which the single figure is a schematic view, partly in cross-section, of an oscillation generator system embodying the principles of our invention.

Referring in detail to the drawing, an ultra short wave generator I, which is shown for the purposes of illustration as of the magnetron type, is connected to an output channel shown as a wave guide 2 leading to a resonating cavity 3 or other type of work device. The generator 1 comprises a central electron-emissive filament ll positioned in the axis of. an anode having the general form of a cylinder with a central chamber 5 from which radial cavities 6 having closed peripheral end walls project. High frequency generators of this type are well known in the art under the term magnetron, and it is believed that morev detailed description is unnecessary here. The wave guide 2 projects from one side of the magnetron l and has a duct or passage 1 openingout of oneof the radial cavities 6 at its radially-outward end to permit electromagnetic waves generated within the oscillator I to be propagated out into the wave guide 2.

In accordance with our invention, we provide a second generator ll of high frequency oscillations capableof operating at the same frequency as the mode of vibration desired to be derived from the-generator l. The generator ll may be of any suitable type for this purpose, but to illustrate the principles of our invention, we show it as a second magnetron, although for some purposes sucha generator as a Klystron may be equally or more desirable. The generator H is connected to transmit energy into a second channel I2, which may be another wave guide, provided at its remote end with a load device I3 capable of absorbing energy of the type generated by the oscillator II. For some purposes, it may be desirable to make the load device I3 adjustable.

The wave guide 2 and the wave guide l2 are connected to each other through a duct M which is of such dimensions as to couple the two wave guides to each other loosely. In fact, so loose may be this coupling that only a fraction of the order of 0.0001 of the power flowing through the wave guide 2 will be transmitted through the duct I4 to wave guide I2. Since the major part of the build-up time of the vibration energy in a magnetron takes place at very low power levels, the flow of an extremely small amount of power through the duct I4 from the generator I I will be sufficient to determine the frequency and mode of vibration at which the generator I will build up at the beginning of each pulse.

In one species of our invent on the generator fl is operated continuously at the frequency corresponding to the mode of vibration desired from oscillator I and is. accordingly, in a condition to transmit through the duct I4 an amount of power sufficient to build up the desired mode of vibration in the oscillating generator I at the beginning of each pulse-period in which power is switched on to the latter to cause the generation of a pulse of vibratory energy to be initiated. Because of the looseness of the coupling provided by the duct I 4, the initiation or cessation of flow of. power from generator I through the wave guide 2 to the load 3 will cause no deleterious interference with the oscillation of the generator I I.

For certain purposes it may be desirable that the oscillation generator II shall not be of the continuously operating type, but it may be switched into operation periodically; and when this is done, it is desirable that the switching operation to energize the generator II should take place a fraction, such as of a pulse duration earlier than the switching in of energizing power to the generator II. It will be obvious that the load I3 will waste almost none of the energy produced by the generator I by reason of the loose coupling above mentioned as existing through the duct I'd.

While we have described the duct I4 as loosely coupling the wave guides 2 and I2, it may be desirable when the generator II is of low power output, as present day Klystron oscillators are, to make this coupling fairly tight, designing the coupling to suit the relative power of the oscillators l and I I. It may be desirable, where this coupling is not very loose, to interpose a TR. switch of conventional type in the duct I4 to cut off power flow through the duct from wave guide 2 to wave guide I2 as soon as the oscillations induced in wave guide 2 by oscillator I have reached a considerable strength. An a plication, Serial No. 480,991, now Patent No. 2,525,468, of Daniel Alpert for Ultra High Frequency Tubes, filed March 29, 1943, shows a TR switch such as is referred to.

We claim as our invention:

1. In combination with a first oscillation generator of a type capable of oscillating in a number of different frequency modes, a transmission system connected to the output thereof, a second oscillation generator connected to a load, and a coupling between said second generator and said first generator providing a relatively loose coupling therebetween.

2. In combination with a first oscillation generator of a type capable of oscillating in a number of different frequency modes and means for causing it to generate energy in successive pulses separated by periods of substantially zero energy, a transmission system connected to the ouput thereof, a second oscillation generator connected to an adjustable load, and a coupling between said second generator and said first generator providing a relatively loose coupling therebetween.

3. In combination with a first high frequency oscillation generator provided with means for causing it to generate energy in successive spaced pulses, a transmission channel conducting energy from said generator to a load device, a second oscillation generator capable of operating at a frequency the same as that at which the first said oscillation generator is desired to act, means for causing said second oscillation generator to transmit energy in pulses having the same perio dicity as those which said first generator produces, means for causing the respective pulses generated by said second generator to be initiated shortly prior to the initiation of each pulse in said first generator, a load device connected through a second transmission channel to said second generator, and means for loosely coupling said first transmission channel and said second transmission channel.

4. In combination with a first oscillation generator of the magnetron type, a transmission system connected to the output thereof, a second oscillation generator connected to a load, and a coupling between said second generator and said first generator providing a loose coupling there between.

5. In combination with a first oscillation generator of the magnetron type and means for causing it to generate enerergy in successive pulses separated by periods of substantially zero energy, a wave guide transmission system connected to the output thereof, a second oscillation generator connected to a load, and a coupling between said second generator and said first generator providing a coupling therebetween.

6. In combination with a first oscillation generator of the magnetron type and means for causing it to generate energy in successive pulses separated by periods of substantially zero energy, a transmission system connected to the output thereof, a second oscillation generator provided with means for causing it to operate with substantial continuity connected to an adjustable load, and a coupling between said second generator and said first generator providing a loose coupling therebetween.

'7. In combination with a first oscillation generator of a type capable of oscillating in a number of different frequency modes and means for causing it to generate energy in successive pulses separated by periods of substantially zero energy, a wave guide transmission system connected to the output thereof, a second oscillation generator provided with means for causing it to operate with substantial continuity connected to an adjustable load, and a coupling between said second generator and said first generator and pro viding a loose coupling therebetween.

8. In combination with a first oscillation generator of a type capable of oscillating in a number of different frequency modes and means for causing it to generate energy in successive pulses separated by periods of substantially zero energy, a wave guide transmission system connected to the o p t means for causing it to operate with substantial continuity connected to a load, and a coupling between said second generator and said first generator and providing a loose coupling therebetween.

9. In combination with a first oscillation generator of the magnetron type and means for causing it to generate energy in succesive pulses separated by periods of substantially zero energy, a wave guide transmission system connected to the output thereof, a second oscillation generator connected to a load, and a coupling between said second generator and said first generator providing a loose coupling therebetween.

10. In combination with a first oscillation generator of the magnetron type and means for caus- 15 ing it to generate energy in successive pulses separated'by periods of substantially zero energy, a waveguide transmission system connected to the output thereof, a second oscillation generator provided with means for causing it to operate with go substantial continuity connected to a load, and a coupling between said second generator and said 6 first generator providing a loose coupling therebetween.

WILLIAM ALTAR. JOHN W. COLTMAN.

REFERENCES CITED The following references are of record in the file of this patents- UNITED? STATES PATENTS OTHER REFERENCES Stabilized Magnetron for Beacom Service, by Donal et a1. RCA Review, June 1947, volume 8, No. 2, pages 352F371. 

